1. Field of the Invention
The present invention relates to a chemical mechanical wafer polishing technique and, more specifically, to a compensating chemical mechanical wafer polishing apparatus and method, which achieves a satisfactory, smooth polishing effect.
2. Description of the Related Art
According to conventional chemical mechanical wafer polishing techniques, the polishing face of the wafer is disposed downwards, and the polishing pad is disposed at the bottom side of the wafer and closely attached to the wafer carrier. The area of the polishing head is greater than the wafer. During polishing, the polishing head covers the whole area of the wafer. This polishing method has numerous drawbacks as outlined hereinafter.
1. High difficulty in end point detection: Because the polishing surface of the wafer faces downwards, the detection of the end point detect is indirectly operated, and the weak detection signal thus obtained must be processed further for reading. If detection is made through the polishing pad or the backside of the wafer, the technical difficulty and cost become high.
2. High consumption of slurry: Because of cover-all architecture, much slurry is used and applied to the broad polishing area of the polishing pad, and most of the slurry are utilized having not contribution to the polishing process, in the other hand, the expensive slurry is misspent. Thus the COO(Cost of ownership) will become high with no meaning.
3. Wafer edge effect: Because the polishing contact pressure is not changed continuously, the edge area polishing of the wafer is ground out significantly, resulting in an edge effect.
4. Bulk and heavy structure: Because of cover-all architecture, the diameter of the polishing head must be greater than the diameter of the wafer. In order to obtain the uniform velocity field on the wafer with the traditional CMP polishing method, the polishing table should be mush larger then the present invention. The heavy weight of the polishing head and platen requires a big scale of driving unit to achieve the desired polishing speed. Therefore, the polishing apparatus requires much installation space and heavy weight.
The present invention has been accomplished to provide a compensating chemical mechanical wafer polishing apparatus, which eliminates the aforesaid drawbacks. It is one object of the present invention to provide a compensating chemical mechanical wafer polishing apparatus, which lowers the difficulty of end point detection, and reduces the cost. It is another object of the present invention to provide a compensating chemical mechanical wafer polishing apparatus, which consumes less amount of polishing fluid, minimizing pollution to the environment and the COO. It is still another object of the present invention to provide a compensating chemical mechanical wafer polishing apparatus, which is compact and not heavy. It is still another object of the present invention to provide a compensating chemical mechanical wafer polishing apparatus, which provides a compensating polishing function to compensate the polishing of the main polishing head. The profile of copper plating on the wafer surface is too complicated to planarize without the dynamic control of different zone pressure with the help of EPD system when traditional CMP tool is utilized, and that is a highly cost and much difficult to compare with present invention. Most of the important things is that compensating method provided a workable method to solve the problem of wafer extension at the edge which is the biggest problem of the traditional CMP apparatus.